This invention relates to multilayer circuit boards, and, more particularly, to multilayer ceramic circuit boards (that is, multilayer circuits formed using ceramic sheets (boards)) and a method for their manufacture.
An example of multilayer ceramic circuit boards is shown in U.S. Pat. No. 3,838,204. In this U.S. patent, an alumina material can be used as the ceramic material, with a conducting pattern formed of a first conductor material, of a refractory metal such as molybdenum (Mo), for instance, and a second conductor material, of copper (Cu), for instance. The conducting pattern of the multilayer circuit boards in U.S. Pat. No. 3,838,204 is formed by forming conductor patterns, using the refractory metal, on a plurality of green sheets of the ceramic and in through holes of such green sheets; laminating the green sheets; and heating the laminated green sheets to sinter them and cause the metal of the conductor patterns to form capillary paths in the patterns; and then placing the sintered structure in contact with a molten, high conductivity metal to allow the metal to enter the capillary paths and fill them, thereby forming the desired high conductivity circuit structure.
When forming the conducting patterns of two layers of conducting material in forming multilayer ceramic circuit boards, for example, a refractory metal layer of tungsten (W) and a highly conducting material layer such as copper (Cu) can be used. However, since adhesion between the W layer and the Cu layer is not so strong, there sometimes occurs peeling between the two different conductor layers. Therefore one problem of such multilayer ceramic circuits with two such conductor layers, directly contacted with each other, is that, due to such peeling, reliability thereof cannot be guaranteed.